By the end of the 13th century, Castilla and Aragón had emerged as Christian Spain's two main powers, and in 1469 these two kingdoms were united by the marriage of Isabel, princess of Castilla, to Fernando, heir to the throne of Aragón. Known as the Catholic Monarchs, they united all of Spain and laid the foundations for the golden age.

In 1478, they established the notoriously ruthless Spanish Inquisition, expelling and executing thousands of Jews and other non-Christians. In 1482, they besieged Granada, and 10 years later the last Muslim king surrendered to them, marking the long-awaited end of the Reconquista. Spain developed an enormous empire in the New World, following Columbus' arrival in the Americas in 1492. Gold and silver came flooding into Spanish coffers from Mexico and Peru as the conquistadors claimed land from Cuba to Bolivia. Spain monopolised trade with these new colonies and became one of the most powerful nations on earth. However, this protectionism hindered development of the colonies and led to a series of expensive wars with England, France and the Netherlands. When Louis XVI was guillotined in 1793, Spain declared war on the new French republic, but was defeated. In 1808, Napoleon's troops entered Spain and the Spanish Crown began to lose its hold on its colonies. Sparked by an uprising in Madrid, the Spanish people united against the French and fought a five-year war of independence. In 1813, the French forces were finally expelled, and in 1814 Fernando VII was restored to the Spanish throne. Fernando's subsequent 20-year reign was a disastrous advertisement for the monarchy. During his time, the Inquisition was re-established, liberals and constitutionalists were persecuted, free speech was repressed, Spain entered a severe economic recession and the American colonies won their independence. The disastrous Spanish-American War of 1898 marked the end of the Spanish Empire. Spain was defeated by the USA in a series of one-sided naval battles, resulting in the loss of Cuba, Puerto Rico, Guam and the Philippines, Spain's last overseas possessions. Spain's troubles continued during the early 20th century.

In 1923, with the country on the brink of civil war, Miguel Primo de Rivera declared himself military dictator and ruled until 1930. In 1931, Alfonso XIII fled the country, and the Second Republic was declared, but it soon fell victim to internal conflict. The 1936 elections saw the country split in two, with the Republican government and its supporters on one side (an uneasy alliance of communists, socialists and anarchists, who favoured a more equitable civil society and a diminished role for the Church) and the opposition Nationalists (a right-wing alliance of the army, the Church, the monarchy and the fascist-style Falange Party) on the other. The assassination of the opposition leader José Calvo Sotelo by Republican police officers in July 1936 gave the army an excuse to overthrow the government. During the subsequent Civil War (1936-39), the Nationalists received extensive military and financial support from Nazi Germany and fascist Italy, while the elected Republican government received support only from Russia and, to a lesser degree, from the International Brigades, made up of foreign idealists. Despite the threat of fascism, England and France refused to support the Republicans.